CLIMATE CHANGE AND AFRICAN AGRICULTURE
Policy Note No. 36, August 2006, CEEPA
Climate change and crop
water use and productivity in
Burkina Faso1
This study examined soil water balance,
crop water use and crop production in
six provinces of Burkina Faso. The
research also draws conclusions
regarding overall climatic trends and
possible ways of adapting to climate
change.
The research implemented by a national
team under the FAO leadership
developed a unified approach in crop
simulation modeling of the relationship
between yield and evapotranspiration as
the measure of water use by crop
agriculture. The country team adapted
the FAO’s CROPWAT program to
assess potential and actual crop water
use of selected crops in six provinces of
Burkina Faso. The simulation of yield
reduction and estimation of crop use was
based on climatic data provided by the
National Meteorological Service. These
are monthly averages for the minimum
and maximum temperature, relative
humidity (minimum and maximum),
1
This Policy Note is prepared by S Perret based
on Some, Dembele, Ouedraogo, Kambire &
Sangare (2006), Analysis of crop water use and
soil water balance in Burkina Faso using
CROPWAT, CEEPA Discussion Paper No. 36,
CEEPA, University of Pretoria.
sunshine, wind speed, rainfall and
geographic
coordinates
(altitude,
latitude, longitude) for the period 1963–
2003.
Climatic conditions and agriculture in
Burkina Faso
Located in the semi-arid tropical zone in
West Africa, Burkina Faso stretches
from the ninth to the fifteenth parallel in
the northern latitudes. The country is
subject to a high degree of both climate
variability and population growth (2.3%
per annum). Its main climatic features
are a low level of rainfall that is also
spatially and temporally variable, and
high temperatures and a high level of
evapotranspiration, particularly during
the dry season. On the whole, the
temperatures and temperature ranges
increase from the south to the north.
There is latitudinal sliding of all isohyets
towards the south, translating to a
reduction of 100mm in average rainfall.
During the last few decades, the 400mm
isohyets rose up to the northern border
of the country and the 1100mm isohyets
reappeared in the south. This rainfall
dynamic has implications for crop
production and food security in Burkina
Faso. Beyond the Sahelian zone, the
dryland Sudanian savanna, which
registers an average annual rainfall
greater than 600mm, has also
experienced serious climate shocks,
particularly droughts, since the early
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1980s. These climate shocks, and
growing demands for natural resources
by
an
expanding
population,
compromise the sustainability of the
current systems of land use and seriously
threaten food security among rural
populations. Massive degradation of soil
chemical and physical status constitute
another threat to agricultural production,
and excessive runoff and low infiltration
reduce the effectiveness of rainfall and
increase water stress.
Case study areas, farming systems and
crops studied
Smallholder,
family-based,
rainfed
agriculture forms the backbone of
Burkina Faso’s economy. Livestock
production supplements crop production
for livelihood and social returns. In most
provinces, millet and sorghum (in sandy
uplands and drier areas), maize, and
occasionally rice (in low and wet lands)
are the main food crops. Other food and
cash crops include groundnut, cowpea,
sesame, soybean, yam, sweet potato, and
a variety of marketable vegetables,
tubers and starch crops when water
availability allows. Cotton is the typical
cash commodity crop in Burkina Faso,
while tobacco is occasional.
One study area was chosen per agroecological zone, as shown in Figure 1.
The provinces (and sites) studied were
Houet (Bobo-Dioulasso) and Poni
(Gaoua), which represent the most
favourable
agricultural
conditions,
Gourma (Fada N’Gourma), Kadiogo
(Ouagadougou)
and
Yatenga
(Ouahigouya), which represent the
Sudano-Sahelian conditions, and Seno
(Dori), which represents the typical
harsh Sahelian conditions. The average
annual rainfall of these sites is 1042mm,
1069mm, 818mm, 756mm, 617mm, and
480mm, respectively.
Besides low averages in annual rainfall,
inter-annual variability in precipitation
and temperature is marked, especially in
Yatenga (Ouahigouya). A declining
trend in rainfall that started with
repeated droughts in the 1980s is even
more worrying. The Sahelian conditions
endured at Seno (Dori) are markedly the
driest.
To reflect the reality of cropping systems
in the selected provinces, a limited
number of crops were selected: cotton,
groundnut, maize and sorghum in BoboDioulasso, Gaoua, and Fada N’Gourma,;
cowpeas, maize and sorghum in
Ouahigouya and Ouagadougou; and
cowpeas, sorghum and millet in Dori.
Simulating crop yield response to
evapotranspiration
The program used for simulating crop
yield response to water (CROPWAT) is
a decision support system developed by
the Land and Water Development
Division of the FAO. Its main functions
are to calculate reference evapotranspiration, crop water requirements
and crop irrigation requirements in order
to develop irrigation schedules under
various management conditions and
scheme water supply and to evaluate
rainfed production, drought effects and
efficiency of irrigation practices. It uses
procedures for predicting yields when all
the climate, soil and crop parameters are
known. This approach allows estimation
of actual evapotranspiration (ETa or
actual crop water use), after having
estimated the stress factor Ks from the
ratio of actual to potential yield.
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In Burkina Faso, the input data for the
model are monthly climatic parameters
including minimum and maximum
temperature, humidity, sunshine and
wind speed. CROPWAT calculates
reference
evaporation
ETo
and
maximum crop evapotranspiration ETm
from crop coefficient Kc. The water
stress coefficient Ks further lowers ETm
to actual evapotranspiration ETa owing
to lack of water. Ks is determined via a
comparison between actual yields Ya
and maximum yields Ym, using a yield
response factor Ky.
Crop water use and productivity in
Burkina Faso
Table 1 sums up the results of
CROPWAT simulations for selected
crops in the study sites. As expected,
calculated crop water use in these sites
reflects the differences in rainfall
conditions and in evaporative demand.
First, optimum crop water demand
increases according to climatic patterns,
i.e. ETm increases (and rainfall
decreases) from southwestern areas
towards
northeastern
Sahelian
conditions. For example, ETm for
sorghum is 413mm and 405mm for
Bobo–Dioulasso and Gaoua respectively; it increases to 422mm and 467mm
for Fada N’Gourma and Ouagadougou
respectively; and finally reaches 529mm
and 556mm at Ouahiyouya and Dori
respectively. Actual water consumptions
(ETa) follow similar patterns for all
crops, with even more marked relative
differences.
Interestingly, crop water productivity
and actual consumption figures also
follows the same pattern, with striking
repeatability: in the southwestern sites of
Bobo-Dioulasso and Gaoua, a cubic
meter of water allows for the production
of about 1.77kg of dry sorghum grain; in
the Sudano-Sahelian central sites
(Ouagadougou and Fada N’Gournma), it
allows for the production of 0.9kg; in
northeastern
Sahelien
conditions
(Ouahiyouya and Dori), it allows for the
production of 0.32kg. In such dry
conditions, millet naturally competes
with sorghum as staple food crop, as its
water productivity remains relatively
much higher (at 1.27kg/m3), for similar
yields. This reflects a much better
adaptation to drought.
Although grown in the relatively better
conditions of the southwestern areas,
cotton exhibits the lowest water
productivity of all crops tested. Cowpea
is also very sensitive to poor
precipitation, with very low yields and
poor water productivity in all stations.
Conclusions and implications
Agricultural production in Burkina Faso
faces two climate-related issues.
On the one hand, low, unreliable (high
inter-annual variability) and declining
rainfall threatens crop production and
forces smallholder farmers to adopt
alternative crops and varieties. Efforts
should be intensified to support water
resource and small-scale irrigation
development wherever possible and to
promote drought-resistant crops and
varieties.
In the southern part of the country,
represented by the weather stations in
Bobo and Gaoua, water requirements
(ETm) for cereal crops and groundnut
are more easily met by the rainfall. In
the Sudano-Sahelian and Sahelian
regions, water deficits are experienced
towards the end of the rainy season.
Supplementary irrigation is needed to
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enable cereal crops to finish their cycle
normally. In the cotton belt, irrigation
needs for cotton and maize are very low,
but in the center, the north and the Sahel,
irrigation needs at the end of the season
are substantial.
On the other hand, soil degradation
occurs in most provinces, owing to the
declining use of organic and chemical
fertilizers, and to erosion.
Farmers have adapted their practices to
such conditions (e.g. using the zai
planting technique to locally improve
soil organic status, contour ridges to
absorb runoff). These water and soil
conservation measures appear to be very
effective for collecting and redistributing
water in the soil. However, the data and
information necessary to inform their
decisions and to further promote
technology change are missing: i.e. crop
water requirements, needs for irrigation,
and variations in soil water balance
according to variations in climatic and
rainfall data for the various agro-climatic
regions of Burkina Faso.
The results of the first phase of study
may be used as an initial picture, to
which climate change scenarios can be
applied. For this purpose, the FAO has
developed under this project a draft
methodology
that
would
allow
CROPWAT to be used to analyze the
effect of climate change on crop water
requirements.
Figure 1: Selected provinces for the study in Burkina Faso
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Table 1: Summary of water use by selected crops in the studied regions
Province
Houet
Poni
Gourma
Seno
Kadiogo
Yatenga
Crops
ETo
(mm)
ETm
(mm)
Ya
(t/ha)
Ym
(t/ha)
ETa (mm)
CWP at
ETm
(kg/m3)
CWP at
ETa
(kg/m3)
Sorghum
412.84
412.80
1.00
Cotton
822.35
797.20
1.04
4.50
56.55
1.09
1.77
2.50
375.26
0.31
Maize
494.35
494.40
1.66
0.28
7.50
186.49
1.52
0.89
Groundnut
515.12
513.00
0.87
2.00
100.04
0.39
0.87
Sorghum
406.31
404.70
1.03
4.50
58.01
1.11
1.78
Cotton
747.40
745.50
0.78
2.50
280.31
0.34
0.28
Maize
476.78
475.30
0.82
7.50
136.39
1.58
0.60
Groundnut
515.49
513.50
0.96
2.00
130.67
0.39
0.73
Sorghum
424.04
422.40
1.03
3.00
114.61
0.71
0.90
Cotton
790.85
788.80
0.89
1.50
497.18
0.19
0.18
Maize
506.48
504.80
1.21
3.50
240.61
0.69
0.50
Groundnut
547.84
545.60
0.98
1.20
402.11
0.22
0.24
Sorghum
558.52
555.90
0.59
1.50
182.10
0.27
0.32
Millet
592.75
592.80
0.60
3.50
47.42
0.59
1.27
Cowpea
552.00
549.10
0.45
1.50
182.85
0.27
0.25
Sorghum
478.84
467.20
0.84
3.00
92.84
0.64
0.90
Maize
575.60
573.00
0.78
3.50
217.03
0.61
0.36
Cowpea
486.21
483.30
0.55
1.50
161.10
0.31
0.34
Sorghum
531.43
529.40
0.67
1.50
202.47
0.28
0.33
Maize
621.65
619.20
0.67
3.50
218.67
0.57
0.31
Cowpea
542.11
539.30
0.45
1.5
179.77
0.28
0.25
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The agricultural sector in sub-Saharan Africa is predicted to be especially vulnerable to climate
change because this region already endures high heat and low precipitation, provides the livelihoods
of large segments of the population, and relies on relatively basic technologies, which limit its
capacity to adapt. This series of Policy Notes reports on the methods and results of the first
continent-wide study of this kind assessing how the economic well-being of African farming
communities is currently affected by climate, predicts how future climate change effects may unfold
under various possible global warming scenarios, and evaluates the roles adaptation to climate
change could play. The study is based on collaborative research efforts conducted in 11 countries:
Burkina Faso, Cameroon, Egypt, Ethiopia, Ghana, Kenya, Niger, Senegal, South Africa, Zambia and
Zimbabwe. The sampled districts used as the unit of analysis cover all key agro-climatic zones and
farming systems in Africa. This is the first analysis of climate impacts and adaptation in Africa on
such a scale and the first in the world to combine cross-country, spatially referenced survey and
climatic data for conducting an analysis that uses economic impact assessment methods, river-basin
hydrological modeling and crop growth simulation techniques.
All the reports produced under this GEF/WB/CEEPA funded project, Regional Climate, Water and
Agriculture: Impacts on and Adaptation of Agro-ecological Systems in Africa, are found on CEEPA
e-Library at its website link (www.ceepa.co.za/discussionp2006.html) and can also be accessed directly
through the project link (www.ceepa.co.za/Climange_Change/project.html)
Centre for Environmental Economics and Policy in Africa (CEEPA), University of Pretoria, Room
2-7, Agricultural Annex, 0002 PRETORIA, South Africa. Tel: +27 (0)12 420 4105, Fax: +27 (0)12
420 4958, Web address: www.ceepa.co.za
Core funding from the GEF and supplementary funding from TFESSD, Finnish TF, NOAA-OPG,
and CEEPA in support of this project’s activities are all gratefully acknowledged. The project was
coordinated by CEEPA and managed in the World Bank by the Agricultural and Rural Development
Department and World Bank Institute.
The findings, interpretations, and conclusions expressed herein are those of the author(s) and do not
necessarily reflect the views of the Board of Executive Directors of the World Bank or the
governments they represent. The World Bank does not guarantee the accuracy of the data included in
this work. The boundaries, colors, denominations, and other information shown on any map in this
work do not imply any judgment on the part of the World Bank concerning the legal status of any
territory or the endorsement or acceptance of such boundaries.
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